In a fresh letter to Brydon, sent yesterday, Hohn accused the LSE board of presiding over a "corporate governance crisis" and expressed his frustration over an agreement that he claims is preventing Rolet from speaking out.

He said the board appears to be threatening a "character assassination" of Rolet.

"It appears to us that Xavier Rolet is being improperly threatened by the board with severe reputational damage unless he steps down... or publicly confirms that he does not want to remain as CEO," Hohn said.

He added: "His silence speaks loud and clear to shareholders that he wants to continue."

The letter was responding to media reports that the board could publish a dossier criticising Rolet's conduct.

The LSE board faces a crunch shareholder meeting by the end of the year – which the LSE must call within the next fortnight – to vote on a resolution put forward by Hohn to remove Brydon from his post.

Hohn’s hedge fund, The Children's Investment (TCI) fund, is trying to drum up support from other large investors for Hohn’s efforts to remove Brydon. He has already received public backing from Egerton chief investment officer John Armitage.

Yesterday’s letter to Brydon said: "The corporate governance crisis which you have presided over has led to significant operational risk for [the] LSE Group, which cannot be tolerated in a systemically important financial institution.

"The situation cannot wait for several weeks until the general meeting... It seems to us that the Bank of England and the FCA both need to immediately intervene to instruct the board to appoint a new chairman who should be tasked with solving this corporate governance crisis."

An LSE spokesperson said: "In requisitioning the extraordinary general meeting, TCI triggered a process which we are now adhering to. The next step in that process is to issue a circular, in order that all shareholders have the same amount of information at the same time.

The row comes at a crucial moment for the LSE, as its dominant euro-denominated derivatives clearing business faces intense political pressure to relocate to the EU after Brexit, in a threat to thousands of jobs within the City of London.

A member of the board of the German central bank, the Bundesbank, today said it was "essential" for "third-country" firms to move their euro clearing operations within the EU.

Speaking in Frankfurt, Carl-Ludwig Thiele said: "It seems to me absolutely imperative that a third-country CCP [central counterparty clearing house], if it poses significant risks to the EU and the euro, ultimately must relocate its euro clearing business within the EU."